/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.primitives;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.Serializable;
import java.math.BigInteger;
import javax.annotation.Nullable;

/**
 * A wrapper class for unsigned {@code long} values, supporting arithmetic operations.
 *
 * <p>
 * In some cases, when speed is more important than code readability, it may be faster simply to
 * treat primitive {@code long} values as unsigned, using the methods from {@link UnsignedLongs}.
 *
 * <p>
 * See the Guava User Guide article on
 * <a href="https://github.com/google/guava/wiki/PrimitivesExplained#unsigned-support">unsigned
 * primitive utilities</a>.
 *
 * @author Louis Wasserman
 * @author Colin Evans
 * @since 11.0
 */
@GwtCompatible(serializable = true)
public final class UnsignedLong extends Number implements Comparable<UnsignedLong>, Serializable {

    private static final long UNSIGNED_MASK = 0x7fffffffffffffffL;

    public static final UnsignedLong ZERO = new UnsignedLong(0);
    public static final UnsignedLong ONE = new UnsignedLong(1);
    public static final UnsignedLong MAX_VALUE = new UnsignedLong(-1L);

    private final long value;

    private UnsignedLong(long value) {
        this.value = value;
    }

    /**
     * Returns an {@code UnsignedLong} corresponding to a given bit representation. The argument is
     * interpreted as an unsigned 64-bit value. Specifically, the sign bit of {@code bits} is
     * interpreted as a normal bit, and all other bits are treated as usual.
     *
     * <p>
     * If the argument is nonnegative, the returned result will be equal to {@code bits}, otherwise,
     * the result will be equal to {@code 2^64 + bits}.
     *
     * <p>
     * To represent decimal constants less than {@code 2^63}, consider {@link #valueOf(long)}
     * instead.
     *
     * @since 14.0
     */
    public static UnsignedLong fromLongBits(long bits) {
        // TODO(lowasser): consider caching small values, like Long.valueOf
        return new UnsignedLong(bits);
    }

    /**
     * Returns an {@code UnsignedLong} representing the same value as the specified {@code long}.
     *
     * @throws IllegalArgumentException if {@code value} is negative
     * @since 14.0
     */
    @CanIgnoreReturnValue
    public static UnsignedLong valueOf(long value) {
        checkArgument(value >= 0, "value (%s) is outside the range for an unsigned long value", value);
        return fromLongBits(value);
    }

    /**
     * Returns a {@code UnsignedLong} representing the same value as the specified
     * {@code BigInteger}. This is the inverse operation of {@link #bigIntegerValue()}.
     *
     * @throws IllegalArgumentException if {@code value} is negative or {@code value >= 2^64}
     */
    @CanIgnoreReturnValue
    public static UnsignedLong valueOf(BigInteger value) {
        checkNotNull(value);
        checkArgument(value.signum() >= 0 && value.bitLength() <= Long.SIZE,
                "value (%s) is outside the range for an unsigned long value", value);
        return fromLongBits(value.longValue());
    }

    /**
     * Returns an {@code UnsignedLong} holding the value of the specified {@code String}, parsed as
     * an unsigned {@code long} value.
     *
     * @throws NumberFormatException if the string does not contain a parsable unsigned {@code long}
     *         value
     */
    @CanIgnoreReturnValue
    public static UnsignedLong valueOf(String string) {
        return valueOf(string, 10);
    }

    /**
     * Returns an {@code UnsignedLong} holding the value of the specified {@code String}, parsed as
     * an unsigned {@code long} value in the specified radix.
     *
     * @throws NumberFormatException if the string does not contain a parsable unsigned {@code long}
     *         value, or {@code radix} is not between {@link Character#MIN_RADIX} and
     *         {@link Character#MAX_RADIX}
     */
    @CanIgnoreReturnValue
    public static UnsignedLong valueOf(String string, int radix) {
        return fromLongBits(UnsignedLongs.parseUnsignedLong(string, radix));
    }

    /**
     * Returns the result of adding this and {@code val}. If the result would have more than 64
     * bits, returns the low 64 bits of the result.
     *
     * @since 14.0
     */
    public UnsignedLong plus(UnsignedLong val) {
        return fromLongBits(this.value + checkNotNull(val).value);
    }

    /**
     * Returns the result of subtracting this and {@code val}. If the result would have more than 64
     * bits, returns the low 64 bits of the result.
     *
     * @since 14.0
     */
    public UnsignedLong minus(UnsignedLong val) {
        return fromLongBits(this.value - checkNotNull(val).value);
    }

    /**
     * Returns the result of multiplying this and {@code val}. If the result would have more than 64
     * bits, returns the low 64 bits of the result.
     *
     * @since 14.0
     */
    public UnsignedLong times(UnsignedLong val) {
        return fromLongBits(value * checkNotNull(val).value);
    }

    /**
     * Returns the result of dividing this by {@code val}.
     *
     * @since 14.0
     */
    public UnsignedLong dividedBy(UnsignedLong val) {
        return fromLongBits(UnsignedLongs.divide(value, checkNotNull(val).value));
    }

    /**
     * Returns this modulo {@code val}.
     *
     * @since 14.0
     */
    public UnsignedLong mod(UnsignedLong val) {
        return fromLongBits(UnsignedLongs.remainder(value, checkNotNull(val).value));
    }

    /**
     * Returns the value of this {@code UnsignedLong} as an {@code int}.
     */
    @Override
    public int intValue() {
        return (int) value;
    }

    /**
     * Returns the value of this {@code UnsignedLong} as a {@code long}. This is an inverse
     * operation to {@link #fromLongBits}.
     *
     * <p>
     * Note that if this {@code UnsignedLong} holds a value {@code >= 2^63}, the returned value will
     * be equal to {@code this - 2^64}.
     */
    @Override
    public long longValue() {
        return value;
    }

    /**
     * Returns the value of this {@code UnsignedLong} as a {@code float}, analogous to a widening
     * primitive conversion from {@code long} to {@code float}, and correctly rounded.
     */
    @Override
    public float floatValue() {
        @SuppressWarnings("cast")
        float fValue = (float) (value & UNSIGNED_MASK);
        if (value < 0) {
            fValue += 0x1.0p63f;
        }
        return fValue;
    }

    /**
     * Returns the value of this {@code UnsignedLong} as a {@code double}, analogous to a widening
     * primitive conversion from {@code long} to {@code double}, and correctly rounded.
     */
    @Override
    public double doubleValue() {
        @SuppressWarnings("cast")
        double dValue = (double) (value & UNSIGNED_MASK);
        if (value < 0) {
            dValue += 0x1.0p63;
        }
        return dValue;
    }

    /**
     * Returns the value of this {@code UnsignedLong} as a {@link BigInteger}.
     */
    public BigInteger bigIntegerValue() {
        BigInteger bigInt = BigInteger.valueOf(value & UNSIGNED_MASK);
        if (value < 0) {
            bigInt = bigInt.setBit(Long.SIZE - 1);
        }
        return bigInt;
    }

    @Override
    public int compareTo(UnsignedLong o) {
        checkNotNull(o);
        return UnsignedLongs.compare(value, o.value);
    }

    @Override
    public int hashCode() {
        return Longs.hashCode(value);
    }

    @Override
    public boolean equals(@Nullable Object obj) {
        if (obj instanceof UnsignedLong) {
            UnsignedLong other = (UnsignedLong) obj;
            return value == other.value;
        }
        return false;
    }

    /**
     * Returns a string representation of the {@code UnsignedLong} value, in base 10.
     */
    @Override
    public String toString() {
        return UnsignedLongs.toString(value);
    }

    /**
     * Returns a string representation of the {@code UnsignedLong} value, in base {@code radix}. If
     * {@code radix < Character.MIN_RADIX} or {@code radix > Character.MAX_RADIX}, the radix
     * {@code 10} is used.
     */
    public String toString(int radix) {
        return UnsignedLongs.toString(value, radix);
    }
}
